Several Mac users have reported an issue in which email accounts (Yahoo or Gmail etc) cannot be added. Users receive the following error message:
Failed to verify the server certificate. This could be because of your network configuration or your proxy settings.
You may also see experience this problem when you want to send or receive mails, because Mail app on your Mac may not connect to your email account.
Even though this error message says this could be because of network or proxy setting issues, users have stated that they are experiencing this problem when in fact there’s no network connection or proxy issues.
Fix Connection Insecure Problem
If you are having this issue, here is how you can troubleshoot:
1-Try temporarily disabling your antivirus software. It is known that sometimes antivirus software may cause this problem. If this solutions does not solve your issue, read on.
2-Expired / revoked SSL certificates may cause this problem. Find and remove them. Here is how you can fix it:
a-Launch Keychain Access (Applications > Utilities).
b-Select “My Certificates”.
c-Now, find expired / revoked certificates, if any. Expired / revoked certificates will have a red X sign. Find also certificates with a red X mark saying “This certificate was signed by an untrusted issuer” or “This certificate was signed by an unknown authority”. When you find them, delete them.
d-When you are done, restart the Mail app.